1. Field
The present application relates to radio frequency (RF) systems and circuits. In particular, the present application relates to methods and systems for providing an RF power splitter with outputs having a desired phase difference (e.g. relative phase).
2. Description of Related Art
In the field of radio and telecommunications, such as, for example, transmission and/or manipulation of RF signals (e.g. in the range of 100 MHz to 100 GHz), it may be desirable to split an input RF signal of a given power amplitude in two signals with a desired phase relationship between the two signals. Such phase relationship can be obtained by shifting each of the two signals by a predetermined phase with respect to the input RF signal, so that the phase difference between the two signals provides the desired phase relationship. In some cases it can be desirable that the two split signals have a desired power amplitude relationship, based on the given power amplitude of the input RF signal, which can result in split signals with a desired relative phase and power relationships. In some cases it can be desirable that the power amplitude relationship provides two split signals of different power amplitudes. In some cases it can be desirable that the power amplitude relationship provides two split signals of same or similar power amplitudes. In some cases it can be desirable to minimize power loss (e.g. insertion loss) during such splitting of the RF signal in two signals, so that the combined power of the two signals is substantially the same (e.g. within 2 dB) as the power of the RF signal. An exemplary embodiment of such splitting function is provided by a hybrid coupler, which as known to the person skilled in the art uses transmission line properties at RF frequencies to divide (e.g. split) an input RF signal of a given power amplitude in two signals of a same power amplitude (e.g. half the power amplitude of the input RF signal) and a desired fixed phase relationship. In some cases, such signals obtained by splitting an RF signal can be used to drive different amplifiers whose outputs can be combined to provide an output RF signal with a desired characteristic, such as, for example, in a case of a Doherty amplifier. The Doherty amplifier may use two signals in quadrature (e.g. 90° phase difference between the two signals) to feed each of its two constituent amplifiers, the carrier amplifier and the peaking amplifier, where the signal feeding the peaking amplifier is at 90° phase with respect to the signal feeding the carrier amplifier. Given the fixed phase relationship between the signals feeding the two constituent amplifiers of the Doherty amplifier, an input RF signal to the latter amplifier can be split using a hybrid coupler, so that each output of the hybrid coupler is connected to a specific constituent amplifier input, and therefore physically linking the outputs of the coupler and the inputs of the constituent amplifiers and thereby imposing certain design and layout rules for a corresponding circuital implementation. More information about a Doherty power amplifier can be found, for example, in reference [1], which is a paper by W. H. Doherty: “A new High-Efficiency Power Amplifier for Modulated Waves”, presented before the Annual Convention of the Institute of Radio Engineers, May 11-13, 1936, at Cleveland, Ohio, which is incorporated herein by reference in its entirety.